Prophase 1

OCR AS-level BiologyCell DivisionLesson 14 of 31

During prophase 1, chromosomes supercoil and condense. They shorten and thicken and become visible under a light microscope as distinct structures.

During the S phase of interphase the DNA has replicated so the appearance of the chromosomes is as two sister chromatids joined by a centromere.

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nucleolus: A spherical structure within the nucleus where ribosomal RNA is made and combined with protein to form ribosomes.
centriole: A structure made of microtubules that organises the spindle fibres during cell division.
interphase: The phase of the cell cycle in which the cell grows, carries out its normal functions and replicates its DNA before division.
chromatid: One of two identical copies of a chromosome, joined by a centromere, formed after DNA replication.
centromere: The region of a chromosome that joins two sister chromatids together and attaches to the spindle fibres.